Does Medical Marijuana Really Reduce Alcohol Crash Fatalities?

Findings from a working discussion paper that links medical marijuana with a reduction in alcohol crash fatalities, published as part of an online labor institute discussion series — not a peer-reviewed study in a scientific journal — are being reported as scientific fact by a surprising number of top newspapers and magazines.

The discussion paper concludes that alcohol traffic fatalities are reduced in medical marijuana states because, as the author’s assert, “alcohol and marijuana are substitutes.” Essentially, the headlines read that because A happened at the same time B happened, A caused B.

There are numerous problems here. (Prevention groups like CADCA have also responded, and rumor is that the White House Office of National Drug Control Policy will also have a response soon).

First, a discussion paper is not a scientific study. It has not been reviewed by scientists, nor submitted for publication to a scientific journal. Until scientists have the opportunity to review the data and the authors’ methodology, their conclusions are preliminary at best. Second, the paper contains several flaws, a few of which are listed here:

The paper ignores the fact that alcohol crash fatalities were already coming down far before the introduction of medical marijuana in any state. (The paper did control for seatbelt and a few other alcohol laws, but it failed to control for many other important factors.) Three decades of education on drunk driving and tough laws have had the direct effect of reducing alcohol-related car crashes dramatically in the last thirty years. In fact, a recent survey by the U.S. Department of Transportation found that 1 in 40 nighttime, weekend drivers tested positive for a blood alcohol content (BAC) level of 0.08 — a 70 percent reduction since 1973. The survey tested other drugs for the first time and found that 1 in 12 tested positive for marijuana. Data from peer-reviewed, published research finds that marijuana impairs motor coordination, reaction time, attentiveness, and perception of time and speed. In a study of seriously injured drivers admitted to a Level-1 shock trauma center, more than a quarter of all drivers tested positive for marijuana. Research conducted at the University of Auckland, New Zealand found that habitual marijuana users were 9.5 times more likely to be involved in crashes, with 5.6 percent of people who had crashed having taken the drug, compared to 0.5 percent of the control group.

The authors studied Rhode Island, Vermont, and Montana “before” (1999-2003) and “after” (2005-2009) medical marijuana. But this is not nearly representative of medical marijuana at all — indeed, in 2009 Rhode Island and Vermont both had under 300 members registered in their medical marijuana programs, respectively, and no medical marijuana dispensaries. In many medical marijuana states there are storefront marijuana dispensaries that sell medical marijuana candy and ice cream. They advertise in the media and are very well promoted and commercialized, notes David Evans, former manager of the New Jersey Intoxicated Driving Program for the New Jersey Department of Health, citing a 2010 New York Times article.

The third state the authors looked at was Montana, which they contend “had more than 27,000″ members in 2011. What they fail to mention, however, is that in 2009, when their study period ends, Montana had only 6,000 members, up from a mere 800 the year before. The vast majority of the growth in the medical marijuana program occurred after the time period studied by the authors.

The authors clearly dismiss or ignore research about the effects of medical marijuana that happen to be inconsistent with their conclusions. A biostatistician and her colleagues at Columbia University looked at 10 states and found increases in marijuana use in medical marijuana states. Another peer-reviewed study found that, though researchers were cautious about speculating why, adolescent marijuana use was higher in states that had medical marijuana.

The authors act as if there were no evidence linking car crashes with marijuana. A meta-analysis to be published in the peer-reviewed 2012 edition of Epidemiological Reviews looked at nine studies conducted over the past two decades on marijuana and car crash risk. Their conclusion? “Drivers who test positive for marijuana or self-report using marijuana are more than twice as likely as other drivers to be involved in motor vehicle crashes.”

There certainly needs to be more research done on the marijuana driving-while-intoxicated link. But to conclude from this working paper, as many media outlets have, that medical marijuana reduces alcohol crash fatalities is both disingenuous and dangerous.